Eye examinations are widely made for the purpose of early diagnosis of life-related diseases or various diseases that are leading causes of blindness. In the examinations and the like, it is necessary to find diseases all over the eye. For this reason, an examination using an image (to be referred to as a broad image hereinafter) in a broader range of an eye is essential. A broad image is obtained using, for example, a fundus camera or an SLO (Scanning Laser Opthalmoscope).
On the other hand, an eye tomogram acquisition apparatus of an OCT (Optical Coherence Tomography) or the like can quantify a disease state based on an objective measure and is therefore expected to be useful for more reliably diagnosing diseases. In a general OCT, an operator decides the tomogram imaging parameters (for example, target part, imaging range, precision level, scanning method, and the like), and images and analyzes only a local eye region based on the imaging parameters.
As a technique of assisting operator's tomographic imaging, for example, patent reference 1 discloses a technique concerning a user interface for designating the tomographic imaging range of an OCT on a broad image obtained by a fundus camera. Patent reference 2 discloses a technique concerning a user interface for designating the tomographic imaging range of an OCT on a broad image obtained by an SLO. According to patent reference 1 or 2, the imaging parameters can be set relatively easily because it is possible to decide the tomographic imaging range while referring to the state of a broad fundus image.
However, the human eye is constantly in an unconscious feeble motion called a small involuntary eye movement even when gazing at a fixed point. The small involuntary eye movement is known to mainly contain three components (feeble motion components) (see FIG. 4).
(1) Tremor: a frequency component of 30 to 100 Hz at a visual angle of about 50°.
(2) Flick: a step- or pulse-like movement which occurs without periodicity (at an interval of about 0.03 to 5 sec) at a visual angle of about 20°.
(3) Drift: a slow movement which exists between flicks at a visual angle of about 10′.
During the measurement processing time of the OCT, a measurement light beam needs to accurately strike a measurement part. Actually, it is difficult to continuously accurately apply a measurement light beam to a measurement part because of, for example, the small involuntary eye movement of the target eye.
Each of patent references 3 and 4 discloses an apparatus which includes a tracking means for moving the irradiation position of a measurement light beam onto a measurement part in real time in correspondence with a small involuntary eye movement.